docs: def render_to_string(self, template_name, context=None):
          """Load and render a template into an unicode string"""
          # create an empty context if no context was specified
          context = context or {}
          tmpl = self.get_template(template_name)
          # render the template into a unicode string (None means unicode)
          return tmpl. \
              generate(**context). \
              render(self.output_type, encoding=None)